It would seem that the reported figure of 1,200 new Metallica riffs is now down to 950 (958 to be precise), as guitarist Kirk Hammett lost the phone that contained 250 fresh musical ideas.

Kirk explained during an appearance on The Jasta Show: "I put riffs on my iPhone, but something very unfortunate happened to me about six months ago. I lost my iPhone [containing] two hundred and fifty musical ideas. And I was crushed."

He continued (via Blabbermouth): "It didn't get backed up. And when it happened, I was bummed out for about two or three days. I walked into the house. My wife saw me and she said, 'Uh-oh, what's wrong? Did you get a phone call from a relative?' I said, 'No.' She said, 'What's going on?' I told her, and she understood.
"I lost [the phone]. I just plain lost it. I can't find it. I'm still looking for it to this day. I just set it somewhere and... It still might turn up. I'm hoping it will. To try to remember those riffs…? I can only remember, like, eight of 'em.So I just chalked it down to maybe it just wasn't meant to be and I'll just move forward with it."
The axeman made sure to point out, "All you musicians out there who use your phone, make sure it's backed up..!

When asked about the sound of new Metallica material, Hammett replied:
"Let's just say that the stuff that's coming up is super riffy, super heavy… We've developed a vocabulary of how we express ourselves through riffs and technique, and let's just say that that vocabulary is well versed. I would say, you know, it's a lot similar to 'Death Magnetic' but different in certain parts. is doing a lot of really, really cool melody stuff these days, a lot of vocal layers.
"'Lords of Summer' is a good example of that, the beginning. And we're just jamming the stuff out. But, yeah, I can say if there's any album that I can compare the stuff that we're working on to, I would say it's a lot like 'Death Magnetic'. And, you know, okay, there's a couple of songs that remind me of something on [1988's] '…And Justice for All', but the album doesn't sound like '…And Justice for All.'"